The present invention relates to an image composing apparatus for connecting a plurality of digital images in which overlap regions of respective end portions of digital images are optimally composed with each other so that one single composition is divided into a plurality of digital images in order to match these digital images with each other, thereby reconstructing a source composition with the matched image.
In general, when one signal composition is divided into a plurality of digital images (binarized image data) for reconstruction of the source composition, portions (end portions) of one digital image and of another digital image to be composed are overlapped on each other, thereby forming an overlap portion (overlap region).
Normally, a dislocation occurs between positions of pixels of an image to compose and positions of pixels of another image to be composed, within the overlap region, and therefore, the positions, densities, and the likes are corrected so that the two images are smoothly connected with each other as a composed continuous image.
For example, Jpn. Pat. Appln. KOKAI Publication No. 63-64180 discloses a method, that is, a matching method, in which, when a large size image is inputted as one single image with use of a hand-scanner, the large size image is divided into a plurality of blocks in order to input the picked-up image since the range of an image which can be picked up by a hand-scanner is limited to a certain area. When such a large size image is reproduced, divided images are superimposed and matched with each other, for all scans, thereby to reproduce the large size image.
In addition, Jpn. Pat. Appln. KOKAI Publication 3-182976 discloses a composing method in which images are converted and binarized such that densities of images to be composed with each other are uniform, and a particular center of particles is obtained for each image, thereby to attain matching of images.
However, in the above publications, a plurality of images are composed with each other by defining an area of a certain range within an overlap region, as a reference block, and on the basis of the reference block, various correction is carried out to compose a plurality of images.
Specifically, there are two conventional methods for defining a reference block, i.e., a method in which a reference block is fixed to a position of a certain area within an image, and another method in which the reference block is manually specified to an arbitrary position of a certain area within an image by an operator. The above-mentioned publication No. 63-64180 discloses a mask pattern in which the block is fixed as in the former method, while the publication No. 3-182976 describes a method like the latter one in which two reference positions are arbitrarily determined by specifying the numbers of pixels of portions expressed in form of particles on an image.
In case where an image compose apparatus is mounted on a camera or the like and is used for purpose of picking up images from presented documents or a block-board used during a meeting, images projected by an over-head projector, or books, there may be a situation that images photographed by the camera must be quickly reproduced, depending on contents of images. Such quick reproduction of images, however, requires high-speed processing, and detection of a reference block and processing for extracting a corresponding point needs to be automatically carried out on the spot after image pick-up operations.
Further, in case of setting a reference block at a fixed position, thereby may be situations that an average density in a reference block is very high (e.g., the number of white pixels is much greater than the number of black pixels, or the reference block is completely white, in case of using binarized images) and the average density in a reference block is very low, since data of images which must be picked up varies. If corresponding points are extracted on the basis of such a reference block, matching cannot be accurately performed.
As described in Jpn. Pat. Appln. Publication No. 63-64180, corresponding points on overlap regions of two images to be composed with each other are extracted such that the points are positioned within a predetermined reference block, and therefore, a large dislocation between images can be smoothly interpolated by setting a larger reference block. However, in this case, processing always requires a long time period.
Therefore, a reference block having a fixed size cannot always have a range from which corresponding points can be properly extracted and which have an effective size.
The method described in Jpn. Pat. Appln. KOKAI Publication No. 3-182976 can be practically adopted to obtain crystal photographs used for investigating a particular metal composition having characterizing particles, but is not designed so as to be applicable for general purpose. Further, since such photographs need not be reproduced after photographing, consideration is not taken into as to measures for shortening a time period required for processing or for achieving high-speed processing. Therefore, high-speed processing cannot be achieved in this method.